The 3D interaction design solution and implementation with VTK and QT were proposed in the system of virtual spinal fixation surgery. After discussing the background of 3D interaction technology, the principles of the interaction design about 3D interaction used in the system was given. According to the requirement of the system, the observer pattern and command pattern were adopted. And then 3D interactive design based on 3D Widgets was given in detail, the implementation view was shown. Finally, some implementation interface and five kinds of widgets design were displayed.